1. Field of the Invention
The present invention Is related to a vehicle anti-theft device, and particularly to a vehicle anti-theft device in which the start-up of the engine is enabled on condition that a predetermined relationship is satisfied by the ID code previously registered in the engine key or the like and the ID code previously registered on the vehicle side.
2. Description of the Prior Art
In some of the various proposals for preventing the theft of a vehicle such as a car, the vehicle is prevented from being started or it is immobilized by mechanical and/or electrical means when it is attempted to be started or moved using a wrong key. This is achieved by previously storing an identification code or a key ID code in a key, reading the key ID code when the key is inserted into a key cylinder to start the vehicle, comparing it with a reference ID code prestored in the vehicle side, generating an enable signal only when there is a match between both ID codes, and enabling the engine to be started up only when an engine control unit successfully receives that signal. In this case, since a theft may be committed by mechanical breakage or illegal wiring if the enable signal is a binary signal of on/off, the encoding of the enable signal has been proposed, for instance, in the "Car Technology", Vol. 48, No. 8, 1994, pp. 59-64.
An example of such a conventional transponder type immobilizer is shown in FIG. 9. A key 2 includes a memory (not shown) in which a key ID code (for instance, of 64 bits) is prestored, and a transmitter 4 for transmitting the key ID code. The transmitter 4 of the key 2 and a key cylinder 5 are coupled together by, for instance, an induction coil (antenna) 6.
When the key 2 is inserted into the key cylinder and rotated to the ignition-ON position, an ignition switch 7 is closed. In response to this, an immobilizer CPU 13 in an immobilizer control unit (ICU) 10 operates, and operating electric power is supplied from a power amplifier 11 to the transmitter 4 through the coil (antenna) 6. The transmitter 4 responds to this to read the key ID code, and transmits it to the key cylinder 5 side.
The received key ID code is detected and digitized by a R/F (radio frequency) circuit 12 in the ICU 10, and read into the CPU 13 and temporarily stored in an appropriate ID code register 13B in the CPU 13. In an EEPROM 13A of the CPU 13, a unique reference ID code assigned to each vehicle is prestored, and tile reference ID code and the key ID code which was read in are compared with each other by a compare unit 13S of the CPU 13. If it is determined that there is a match between the two or they are in a predetermined relationship, an enable code is transmitted from the compare unit 13S to an engine control unit (ECU) 16. At the same time, a starter relay 15 is activated to initiate the rotation of a starter motor (not shown).
When the engine ECU 16 has determined and verified the received enable code, the engine ECU 16 controls a fuel injection valve 17, a fuel pump 18, an ignition control unit 20, etc., according to a predetermined procedure and timing to enable the start and travel of the vehicle.
If the reference ID code stored in the EEPROM 13A and the key ID code transmitted from the key 2 and read in do not match each other or they are not in a predetermined relationship, the compare function unit 13S does not issue an enable code. Accordingly, the start of the vehicle by the ECU 16 is inhibited, and a horn 14 is activated by the CPU 13 to provide an appropriate alarm and display. Thus, the illegal start-up of the engine and the driving of the vehicle by a wrong key are prevented to ensure the vehicle anti-theft function.
However, if an ID code is provided for each key, there must be thousands or tens of thousands of different ID codes, and thus, usually, the maker or seller of keys does not manage keys depending on these ID codes for the convenience of the manufacturing or management of keys. Accordingly, if a user has lost or broken his key, it would be extremely difficult to specify and buy a key having the same ID code. Thus, if a key was lost, it would be necessary to purchase a new key of a different ID code, and newly register the ID code of this new key on the vehicle side.
For the new registration of a key having a new ID code, as described, for instance, in the Japanese Patent Publication No. 3-76077 official gazette, a switch for switching the operation mode to either a "write mode" or a "read mode" for an ID code was provided, and normally, or for operating the anti-theft function, it is switched to the "read mode" side, while for registering the ID code of a new key, it is temporarily switched to the "write mode".
In the above prior art, the switching means for specifying the "read mode" or the "write mode" is indispensable, and the registration of a new key can very easily be done by switching this switch. Accordingly, there is a problem that, if an ill-intentioned third party has got a new key and newly registered it by switching this switch means, the start-up of the engine by the new key is enabled and the theft of the vehicle can easily be accomplished.